The objective of this blinded, randomized, prospective study was to assess whether supplementation of normal diet with omega-3 polyunsaturated fatty acids can reduce angiographically defined restenosis following coronary angioplasty. The study included all patients undergoing coronary angioplasty in this institution between January 1988 and January 1989. One hundred and twenty patients enrolled, 60 in each treatment group. All were randomized to either supplementation of normal diet with 3 g of omega-3 polyunsaturated fatty acids per day started 1-2 days prior to angioplasty and continued for 6 months (treatment group), or to receive standard therapy only (control group). Quantitative angiographically defined restenosis was assessed at 6 months post angioplasty. Restenosis occurred in 27·8% (95% CI18·0-37·7%) of lesions in the treatment group and in 28·3% (CI 16·9-39·7%) of lesions in the control group, but the difference was not statistically significant.The study showed that diet supplemented with 3 g of omega-3 polyunsaturated fatty acids started 1-2 days preceeding angioplasty does not reduce angiographically defined restenosis rate. © 1992 The European Society of Cardiology.